1. Field of the Invention
The present invention generally relates to a LCD skill technology, and more particularly to a light guide plate and a backlight module utilizing the light guide plate.
2. Description of Prior Art
Because the liquid crystal itself of the LCD panel does not provide the characteristics of luminescence, a light source device, such as a backlight module is needed for the LCD panel for achieving the display effect. The function of the backlight module is to provide a surface light source fully brighten and uniformly distributed for the LCD panel.
In prior arts, the backlight module comprises a light source, a light guide plate and some other necessary portions. The function of the light guide plate is to guide the propagating direction of the light to allow the light uniformly emitted through the light-emitting surface of the light guide plate. The light source such as LED is utilized. The structure of an LED is shown in FIG. 1(a) and FIG. 1(b). The structure of the LED comprises a YAG fluorescent powder 10 and a blue light LED chip 20. Alternatively, the structure of the LED comprises RGB fluorescent powder 30 and a UV LED chip 40. The principles for generating white light are mainly categorized as follow four kinds: A. a blue light LED chip+yellow fluorescent powder (such as YAG); B. a blue light LED chip+yellow fluorescent powder+red fluorescent powder; C. a blue light LED chip+green fluorescent powder+red fluorescent powder; D. a UV LED chip+RGB fluorescent powder. Generally, the fluorescent powder is directly coated on the LED chip or uniformly distributed in the package material of the LED itself.
Moreover, the structure of a side light type LED backlight module is shown in FIG. 2: light of a plurality of white LED 110 is guided into a light guide plate 120 from the side thereof. The light propagates in the light guide plate 120 by total reflection. When the light is incident onto the screen dots 130, part of light is diffused by the diffusion particles on the screen dots 130 and emitted through the light-emitted surface over the light guide plate 120.
As aforementioned, the coating of the fluorescent powder in prior art has drawbacks below: First, the LED generates lots of heat in the luminous process. The heat accumulation leads to the fluorescent powder coating portion with higher temperature but the resistance of the fluorescent powder to high temperature is bad and then the ageing is accelerated; besides, the reflecting absorption loss of the reflecting absorption to light also degrades the luminous efficiency of the LED. Therefore, the LED with such coating has drawbacks of fast luminous efficiency degradation, large color shift as time and low luminous efficiency. Please refer to FIG. 3, which shows the lighting effect variation of a LED versus time according to prior art. The Y-axis indicates the luminous efficiency and the X-axis indicates the Celsius. The square spots represent the YAG fluorescent powder and the round spots represent the InGaN blue LED. As shown in FIG. 3, the bad condition that the luminous efficiency changes as time to such kind of LEDs and the high requirement of color in display area come as a paradox.